Blood digestion in the mosquito, Anopheles stephensi: the effects of Plasmodium yoelii nigeriensis on midgut enzyme activities

Midgut proteases contribute to the success or failure of Plasmodium infecti on of the mosquito. This paper examines the reciprocal effect of Plasmodium yoelii nigeriensis on midgut trypsin, chymotrypsin, aminopeptidase and car boxypeptidase in the mosquito Anopheles stephensi. The total protein ingest ed and the rate of protein digestion were unaffected by the parasite, but m ore protein was ingested at the first than the second bloodmeal. All peptid ases were unaffected by the presence of the parasite during the first gonot rophic cycle, when ookinetes were penetrating the midgut. In the second gon otrophic cycle, trypsin and chymotrypsin were unaffected by growing oocysts , but aminopeptidase activity was reduced in the midguts of infected mosqui toes. Chymotrypsin activity was depressed and aminopeptidase activity eleva ted during the second gonotrophic cycle. Plasmodium infection has a negligi ble effect on bloodmeal digestion and does not limit the availability of th e protein for egg production. The significance of changes in aminopeptidase activity when oocysts are present is discussed.